The present invention relates generally to thermophotovoltaic generators, and more particularly but not solely to micro generators.
There is a rapidly growing trend in the miniaturization of mechanical and electro-mechanical engineering devices. All kinds of microdevices such as micro-pumps, micro-motors, micro-robots, micro-rovers and micro-airplanes are being developed. However, the miniaturization of these devices is limited by the weight of the available power systems (batteries) that occupy significant fractions of both mass and volume of the entire devices. Typical portable mechanical devices also suffer from short operating cycles between charges or replacement. The need to reduce system weight and increase operational lifetimes is behind the emergence of a new class of microelectromechanical system (MEMS) devices, micro power generators that are characterized by high power and energy density but small in size and weight, and are cost effective.
It is well known that hydrogen and hydrocarbon fuels have energy densities much greater than the best batteries. For example, hydrogen fuels provide an energy storage density of typically 120 MJ/kg, whereas the state-of-the-art lithium ion batteries commonly used in cell phones and laptop computers provide only about 0.5 MJ/kg. Thus even at only 10% conversion efficiency from thermal to electrical energy, hydrogen fuels are 24 times more powerful than batteries. The advantages of hydrogen fuels also include being inexpensive, having more constant voltage, suffering no memory effect, and being capable of instant recharge. Therefore, taking advantage of the high energy density of chemical fuels to generate power becomes an attractive technological alternative to batteries.
Micro-gas turbine engines, micro-rotary engines (Wankel-type), micro-thermoelectric and micro-fuel cells are typical micro power generators being developed currently. The above micro-power systems experience one major challenge, the high heat losses due to the high surface-to-volume ratio. According to the cubic-square law, when the size of a microdevice decreases by a factor of 100, the surface to volume ratio will increase by a factor of 100. Therefore, with the same heat flux density per unit surface, the heat flux via the wall will increase by a factor of 100 per unit volume of a microcombustor.
Thus, what is needed is a device which ameliorates the difficulties identified in the abovementioned prior art or at least provides the public with a useful choice.